It was almost exactly two years ago that Adam first contacted me about joining him and Marcelo in a science/culture project that morphed, five months later, into NPR's 13.7: Cosmos & Culture. I have loved the experience, the community, the weekly challenge, the encouragement and the critiques, everything about it. I've learned an enormous amount. But I've reached the decision that I need to step aside and join the distinguished cohort of 13.7 readers.

Why? Well, it has everything to do with science.

A while back I outlined a research trajectory we'd initiated to explore the potential of algae — specifically, the green soil alga Chlamydomonas that I've studied for over 40 years — to produce lipids that can be converted to diesel and jet fuel.

At first the experiments were interesting and engaging, yet I had no difficulty putting them aside to devote Wednesday evenings to developing my thoughts for 13.7.

Then things revved up. Collaborations initiated and flourished, new approaches yielded new discoveries that led to more collaborations. Best of all, I've been doing many of the experiments myself, after several decades of supervising the experiments of others, staring through the microscope for hours at gorgeous cells that we've coaxed into becoming fatter and fatter.

Increasingly, as Wednesday evening rolled around and I'd fire up a blank .doc page, it would sit there, staring at me stubbornly, even leeringly, while my mind raced with what I'd seen that afternoon and what the next round of experiments would be.

Will any of this eventually help ease our dependency on fossil fuels? I'd love to think so. But I can't foist responsibility for my leave-taking onto some fantasy of saving the world. Fact is that it's that time-honored, old-fashioned joy of scientific discovery that's pulled me away.

With love to you all and deep gratitude for all that you've given back to me.